In this article, the place of the instinct theory in the classic psychoanalytic view is explained which is defined by Freud as a borderline concept between the psyche and the body. The instinct theory which is one of the most abstract concepts of the psychoanalysis is many times subjected to modifications by Freud. These modifications, not by eliminating each other but by becoming more and more stratified at every turn, bring about the constitution of a rich theory. The instinct theory, by maintaining its ambivalent structure, is first explained as the opposition between the ego's auto-conservation and the sexual instincts. With the putting forward of the importance of narcissism, psychoanalytic theory which drew attention to the link between the “leaning on” and the individual's choice of love objects, pointed out as well the determinism of the human's destiny by explaining the opposition between instincts of life and of death.